This can not work. This is too early for config() to work. These files either need to be replaced with container services or the variable get with global $conf, or whatever we come up with in #1810912: [meta] Decide on pluggability.

session and path have issues already, not sure how much of menu will remain after the conversion to routes.

I suppose there won't be much impact on upgrading sites from D7 if these variables had been changed, so using $conf could be acceptable. If these variables were changed this would mean that the custom code they are pointing to needs to be rewritten as well.

I had checked the issues for session and path before starting this and I believe neither of them were taking care of these variables.

#6 is factually wrong - the config system works before all other systems are able to work. It is the first subsystem that is actually exempt from bootstrap phases (except for the includes/config.inc include).

But regardless of that, these variables are to be converted into service container overrides, not into config.